An Evidence-Based
Approach To Exercise
Prescriptions on ISS
Lori Ploutz-Snyder, Ph.D
Project Scientist & Lab Manager
Exercise Physiology and Countermeasures
Universities Space Research Association
Lyndon B Johnson Space Center
Summary of the Presentation
– Current exercise countermeasures
– New ISS exercise equipment
– Strategy for evaluation of evidence
– Proposed new ExRx
Historic ISS Exercise
• 2.5 hrs/day, 6 days/wk
• Resistance exercise
– iRED
– Predominantly high reps low loads
• Aerobic exercise
– TVIS & CEVIS
– 30 min continuous at ~70% HRmax
– Some interval work – “Greenleaf protocol”
Limitations of ISS Exercise Hardware
• iRED
– Maximal load 300 lbs
– Elastic bungee resistance
not constant
– Limited eccentric
component
Limitations of ISS Exercise Hardware
• CEVIS
– Maximal load 300 Watts
• TVIS
– Speed limitations
– Subject loading limitations
Limitations of ISS Exercise Hardware
• TVIS
– Speed limitations
– Subject loading limitations
Fitness Changes on ISS
• ISS crewmembers
(expeditions 1-15, n=18)
– Isokinetic knee extensor
and flexor strength decrease
11% and 17%, respectively.
– Isokinetic knee extensor and flexor endurance
decrease 10% and 9%.
– Maximal aerobic capacity (estimated from
submaximal test) 10% reduction
– Bone mineral density (BMD) 2-7% decrease
depending on site.
Why?
• ISS exercise hardware does not allow
for sufficient intensity of exercise
• Inadequate ExRx
• Crew member noncompliance with
ExRx
• Other
New ISS Hardware - ARED
• More exercises (29 different ones)
• Instrumented for data acquisition
–
–
–
–
Sets
Reps
Ground reaction forces
Load at the bar
• Improved loading
–
–
–
–
600 lbs
Ecc-Con Ratio ~90%
Constant load
Simulated inertia (free weight)
New ISS Hardware – T2
• Better harness & subject loading system
• Instrumented to record ground reaction
force
• Improved speed
HRP Integrated Research Plan
Risks and Gaps
• Risk of impaired performance due to reduced muscle
mass, strength and endurance.
– Gap M7: Can the current in-flight performance be maintained
with reduced exercise volume?
– Gap M8: What is the minimum exercise regimens needed to
maintain fitness levels for tasks?
– Gap M9: What is the minimum set of exercise hardware needed
to maintain those (M8) levels?
• Risk of reduced physical performance capabilities due to
reduced aerobic capacity.
– Gaps M7-9: (above)
– Gap M2: What is the current status of in-flight and post-flight
performance capability?
– Gap CV2: What is VO2max in-flight and immediately post-flight?
More Risks/Gaps
• Risk of accelerated osteoporosis.
– Gap B15: Can exercise hardware and
protocol be designed to provide loads
necessary to maintain bone health?
Workshops
• June and October 2008 workshops suggested
enough ground-based evidence existed to move
forward with a flight ExRx study.
– ASCR, ExPC, HRP management, flight surgeons, medical
operations, external experts
• Major recommendations
– Higher intensity, less frequent resistance exercise
– More variety of resistance exercises
– Alternate days of moderate intensity continuous aerobic
exercise with higher intensity interval aerobic exercise
– Monitor in-flight exercise performance using instrumented
hardware
– Include more robust physiological outcome measurements to
document the efficacy of the exercise program.
• March 2009 proposal submitted for NAR
Strategy for ExRx
• Identify exercise training programs that have been
shown to maximize adaptive benefits of people
exercising in both 0 and 1 g environments.
• Priority order of evidence
– ISS or spaceflight information
– Human flight analog studies (bedrest, unilateral lower limb
suspension (ULLS).
– Human 1-g exercise training studies
– Animal flight analogs or 1 g studies only in the rare
cases where no human data exist.
Cardiovascular Fitness
• “Capacity of the heart and lungs to
supply oxygen-rich blood to the working
muscles and the capacity of the
muscles to use oxygen to produce
energy.”
www.health.qld.gov.au/npag/glossary.asp
• Evaluation should include more than
VO2max
Intensity Is The Key Factor
• Trained for 10 weeks
– High intensity (90-100% max HR) interval
cycle (6x 5min, 2 min rest) exercise
alternated with continuous running as fast
as possible for 40 min.
• Divided subjects into 3 maintenance
groups where one factor was reduced:
intensity, duration or frequency.
(Hickson et al, 1981, 1982, 1985)
Maintenance Groups
• Intensity
– Work rate reduced by 1/3 or 2/3
• Duration
– Reduced from 40 to 26 or 13 min/day
• Frequency
– Reduced from 6 to 4 or 2 days/week
(Hickson et al, 1981, 1982, 1985)
Which Group Would You Choose?
• Physiological adaptations were most robust to a
decrease in training frequency as evidenced by a
maintained VO2max with as little as 2 days/week of
high intensity exercise.
• Most physiological adaptations were maintained
despite a decreased duration, even with as little as
13 min/day of training. The exception was that longterm (~2hr) endurance was not maintained in the
shortest duration (13 min/day) group, however short
term (~5 min) endurance was maintained.
(Hickson et al, 1981, 1982, 1985)
Intensity Most Important Factor
• Little maintenance of physiologic adaptations with
even the 1/3 reduction in training intensity.
– Despite training 6 days/week for 40 min/day VO2max, longterm endurance, and left ventricular mass were not
maintained with 1/3 reduction in training work rate.
– Alarmingly, all training-induced increases in left ventricular
mass were completely lost when work rate was reduced by
1/3.
– Training HR from 180 to 150 beats/min.
• To minimize crew time spent on exercise, exercise
frequency and duration may be reduced but intensity
must be as high as reasonably possible.
(Hickson et al, 1981, 1982, 1985)
ISS Aerobic Exercise
• Currently 30-40 min at 70-85% HRmax
on CEVIS or TVIS.
• Research overwhelmingly shows higher
intensity is required for physiologic
adaptations.
• Interval work suggested.
Aerobic Intervals
• 20-30 second “all out sprints”
– Shortest well documented training
– Elicits CV adaptations primarily at
peripheral sites
• Increased muscle oxidative enzymes and
mitochondrial biogenesis
– Very short exercise durations
• 8 sets of 20 sec sprint with 10 sec recovery
takes 4 min + warmup/cool down.
Burgomaster et al., 2008; Gibala & McGee, 2008; Gibala et al., 2008; Tabata et al., 1996
Medium Intervals
• 2-3 minute intervals
– Bedrest evidence of maintenance of VO2
max (Lee et al., 2008)
– 2 min interval sometimes used on ISS
• 7 minute warm up at 40% of VO2max, followed
by 5x2 minute stages at 60,70,80,90,80%
VO2max, 5 min cool down (Greenleaf et al., 1989).
• Well tolerated by crew, anectdotal evidence
Long Intervals
• 4 minutes
– Large number of ground based training studies
support 4 min intervals over continuous exercise.
– Best results when intensity is maintained ~90%
– 4x4 min at 90-95% HRmax particularly good for
increasing stroke volume (Helgerud et al 2007).
– Elderly post MI heart failure patients show
increases in VO2max & perform exercise at home.
(Wisloff et al, 2007)
Bone
• Bedrest studies - exercise interventions
effective in reducing some, but not all bone
loss.
– Linearly periodized resistance exercise program and increased
bone mineral density (BMD) in the lumbar spine, preserved bone in
the heel, femoral neck and total hip, but was effective at the
trochanter in only those subjects with dynamic loading of the hip on
single heel raises (Shackelford et al., 2004).
– Fixed traditional training program of leg and calf press using a
flywheel device combined with low body negative pressure (LBNP)
treadmill exercise alleviated about half of the bone loss in the
trochanter and total hip (Smith et al., 2008).
ISS Exercise and Bone
•
•
•
•
•
Evidence from missions on ISS (expeditions 1-15; n=19) show
modest correlations (r=0.4-0.55) with bone mineral density and
time/intensity of exercise.
Trochanter, lumbar spine, and whole body BMD correlated with
total aerobic exercise time above 70% HRmax.
Trochanter and pelvis BMD correlated with total number of total
exercise sessions.
Femoral neck and lumbar spine BMD correlated with total
treadmill exercise time.
Pelvis BMD correlated with IRED deadlift load used during
training, but other IRED correlations were much lower
(unpublished internal data).
Bone
• High magnitude (Rubin & Lanyon, 1985) and rate of
dynamic (not static) strain (Hsieh & Turner, 2001).
– Periodized resistance training program where the
magnitude and rate of strain is regularly altered.
• Diverse strain distributions as bone
adaptations are well documented to be site
specific in humans as evidenced by both in
vitro (Bass et al., 2002) and in vivo investigations (Maple et
al, 1997; Winters-Stone & Snow, 2006).
– Periodized resistance training whereby the
resistance exercises are varied to yield diverse
strain distributions.
Bone
• Only a few repetitions are required (Rubin & Lanyon, 1984).
– 36 cycles of loading per day is as effective as 360
cycles/day when the strain rate is high.
– Minimal number of repetitions is dependent on the
load, with higher loads requiring fewer repetitions
(Cullen et al, 2001)
– 2 shorter higher intensity exercise sessions in one
day as opposed to one longer session
Bone
• Multiple daily exercise sessions optimize
bone growth (Robling et al., 2000).
– Resting ~4 h between bouts nearly doubled bone
formation responses in rodents (Robling et al. 2001).
– Significant correlations among trochanter and
pelvis BMD and total number of exercise sessions
on ISS.
– Femoral neck and lumbar spine BMD correlated
with total treadmill exercise time on an ISS.
– 2 exercise sessions in one day as opposed to one
longer session; maximize intensity
Bone
• Longer rest intervals between sessions
and sets is beneficial.
– Bone quickly sensitizes to the mechanical loading
stimulus, allowing rest periods between sessions
allows for restoration of the mechanosensitivity.
– 8 hours of recovery is required to regain full
mechanosensitivity of bone & 14 seconds is the
optimal time between loading cycles within an
exercise session in rodents. (Robling et al., 2001).
– This supports the notion of having 2 exercise
sessions in one day separated by several hours
as opposed to one longer session
Muscle
• >25 bedrest and ULLS studies evaluating
exercise as a countermeasure for muscle
size/strength
• Variety of exercises used
– LBNP treadmill
– Flywheel
– Traditional weights
• All exercise programs that were effective in
maintaining muscle size/strength used
maximal or nearly maximal contractions.
Examples of Effective Countermeasures
• Traditional weights
– 21 day ULLS KE and PF
– 10 reps at 40%, 2 MVIC, 10 reps at 80%, a
final set of as many reps as possible of
isotonic exercise at 80%.
– Every 3 days
– Total exercise time (including rest) was 6.5
min
– KE and PF CSA and MVC were maintained
Schulze et al., 2002
Countermeasures
• Traditional weights
– 14 Days Bedrest
– 5 sets of leg press every other day at 8 RM
– 1RM & CSA maintained, MVIC not
Bamman et al., 1998
Countermeasures
• Inertial flywheel
• 60 Day bedrest exercise for squat & calf
press every 3 days beginning on day 2
• LBNP treadmill
• Effective to maintain VL size and
strength but not SOL (28% vs 8% loss)
(Trappe et al., 2007, 2007, 2008)
Common To Effective Countermeasures
• Use of maximal or nearly maximal
contractions!
• Calf and thigh require different stimuli
Countermeasures
• So…how do you design exercise
programs for spaceflight?
• If it works in bedrest does it work with
spaceflight?
Flight Countermeasures Improving
• NASA/MIR – elastic expanders
– 16 crew, ~140 days, 10%, 13% loss in
muscle mass in QF and calf
• ISS – IRED
– 18 crew, ~180 days 11%, 18% loss QF,
calf strength
QuickTime™ and a
DV/DVCPRO - NTSC decompressor
are needed to see this picture.
Bedrest vs. Spaceflight
• Length of study
– Few bedrest studies as long as 90 days
– ISS flights 180 days
• Presence of gravity in bedrest
– Movements in bed still against gravity
– Lumbar spine
– Other stressors in flight, calm & safe in
bedrest
Exercise Equipment on ISS
• Advanced Resistance Exercise Device
(ARED)
ARED
• Greater loads – 600 lbs
– Pneumatic cylinders
• Constant load
• Ecc-Con ratio ~90%
– Flywheels
• Simulated inertia
• 29 different exercises
• Instrumented
ISS Exercise Equipment
• TEVIS
• CEVIS
• T2 soon
Resistance Exercises – Weekly Schedule
Day 1
Squat, Bench Press,
Romanian Dead Lift,
Upright Row, Heel Raise
Day 2
Dead Lift, Shoulder Press,
Single Leg Squat, Bent-over
Row, Single Leg Heel Raise
Day 3
Front Squat, Bent-over
Row, Single Leg Knee
Extension, Bench Press,
Heel Raise
Week
1
Light
Light
Light
2
Light
Light
Light
3
Moderate
Light
Heavy
4
Heavy
Moderate
Light
5
Light
Heavy
Moderate
6
Moderate
Light
Heavy
7
Heavy
Moderate
Light
8
Light
Heavy
Moderate
9
Moderate
Light
Heavy
10
Heavy
Moderate
Light
11
Light
Heavy
Moderate
12
Moderate
Light
Heavy
Resistance Exercise Session Details
Weeks 1-6
Light
Moderate
Heavy
Sets
3
3
3
Reps
12
8
5
Rest (sec)
90
120
120
Total Time (min)
35
40
40
Light
Moderate
Heavy
Sets
3
4
4
Reps
10
6
3
Rest (sec)
90
150
180
Total Time (min)
35
50
60
Weeks 7-12
Aerobic Interval Exercises
• Short Sprint - 10 minute warm up at 50% of HRmax, followed by
7-8 sets of maximal exercise for 30 seconds, followed by 15
seconds rest. Increase load after 9 sets
• 2 minute - 5 minute warm up at 50% VO2max, followed by 6x2
minute stages at 70, 80, 90, 100, 90%, 80% VO2max. The first 5
stages are separated by 2 minute active rest stages at 50% VO2
max. The final stage is a 5 min active rest at 40% VO2max.
• 4 minute - 5 minute warm up at ~50% HRmax, followed by
intervals of exercise at 90% HRmax. The exercise intervals will be
4x4 min bouts, with 3 min active rest periods.
Integration of Resistance and Aerobic
Day
1
Resistance
35-60
min
Day
3
30
min
Day
4
35-60
min
32
min
Aerobic Interval
Aerobic Continuous
Day
2
Day
5
35-60
min
15
min
30
min
Day Day
6
7
35
min
30
min
Note: Time savings up to 3 hours/week compared to current exercise time
At least 4 hrs, preferably 8 hrs separating exercise sessions
Pre- and Post-Flight Measurements
• Muscle CSA
– Pre/Post-flight MRI – Availability at landing?
– Pre/In/Post-flight Ultrasound – In-flight?
• Muscle Function Test from FTT
– Power, endurance, CAR, steadiness
• Single fiber size, contractile function, type
• Aerobic & glycolytic enzymes
– Citrate synthase & PFK
Pre- and Post-Flight Measurements
•
Cardiovascular
– Pre/In/Post-flight VO2max
– Ventilatory threshold pre/post-flight using standard ramp cycle
protocol
• 50 Watts for 3 min then increased by 25 Watts/min thereafter
– HR response to submax load pre/in/post
– US for cardiac contractility
•
Bone
– QCT as a standard medical test. Structural parameters can be
estimated from 2-d DXA scans by hip structure analysis in the
absence of QCT scans.
– Request data sharing with with MedB8.1/Clinical Nutritional
Assessment and the SMO 016E/Nutritional Status Assessment for
bone markers.
Pre-Post-Flight Test Schedule
Time
Test
Time Required
Preflight L<365
Bone
60 min
Preflight L-180
Isokinetic knee, ankle, back
75 min
Preflight L-60-90
Isokinetic knee, ankle, back
60 min
Preflight L-50-55
Biopsy
60 min
Preflight L-45-50
MRI, US , functional
fit=Muscle, Cycle=VO2max
60, 50, 30, 60
min
Preflight L-10
MRI, Muscle, US, VO2max
60, 50, 30, 60
min
Postflight R+0
MRI or US, Biopsy
30 min, 60 min
Postflight R+1
Muscle, VO2max
50, 60 min
Postflight R+5
Isokinetic knee, ankle,
functional fit =Muscle
60,60 min
Postflight R+6
MRI, US
60, 40, 30 min
Postflight R+10
Cycle =VO2max
60 min
Postflight R+14
Isokinetic knee, ankle, back
60 min
Postflight R+29
Cycle =VO2max
40, 60 min
Postflight R+30
Isokinetic knee, ankle, back,
functional fit = Muscle
60, 60 min
Postflight <R+30
Bone
60 min
•In-flight Data
Muscle Strength
5 RM weeks 1-7
3RM after week 7
VO2max
Every 30 days
Muscle Size??
Vastus lateralis
via ultrasound
Pre-flight testing = 11
hrs
Post-flight testing=
14 hrs
Summary
• New ISS exercise hardware should
allow for exercise at intensities high
enough to be expected to elicit adaptive
responses and provide quantitative
information about loading.
• New ExRx should incorporate higher
intensity exercises and seek to optimize
intensity, duration and frequency to
yield an efficient ExRx.